new line in character

I'm just starting to learn this lisp stuff so please go easy one me.

I'm having a slight issue maybe someone can help me understand.

Command: (setq test (strcat "hello" "\n " "there"))

"hello\n there"

I read in the help documentation that \n is a new line

but it doesn't display as such with my example.

Am I misunderstanding how to use the new line character.

I'm just playing around learning this so it has no meaning but I was just trying to display

hello

there

Thanks

Hi John,

"\n" is indeed the New line character, try running these to experiment:

(defun c:test ()
 (princ "\nMy Name is \nJohn")
 (princ))

Hope this helps

Lee, does (princ) and (strcat) process control codes differently? I noticed a similar thing when I tried:

(strcat "\010" " " "\010")

That is to say, I couldn't princ it, I -had- to strcat it in order for it to work the way I wanted it to.

Octal Codes seem to work for me -

for example:

(princ "\100Lee Mac")
(princ)

Returns:

@Lee Mac

But Control Characters are harder to test for, so I'm not sure.

(strcat) doesn't evaluate the code, it just concatenates the strings.

(princ) evaluates the string control characters prior to displaying them

You can see the biggest differences between (prin1) (princ) and (print) when outputting to files

 [b][color=BLACK]([/color][/b]setq wf [b][color=FUCHSIA]([/color][/b]open [color=#2f4f4f]"text.txt"[/color] [color=#2f4f4f]"w"[/color][b][color=FUCHSIA])[/color][/b][b][color=BLACK])[/color][/b]
 [b][color=BLACK]([/color][/b]princ [color=#2f4f4f]"\nPRINC call"[/color] wf[b][color=BLACK])[/color][/b]
 [b][color=BLACK]([/color][/b]write-line [color=#2f4f4f]" - "[/color] wf[b][color=BLACK])[/color][/b]
 [b][color=BLACK]([/color][/b]prin1 [color=#2f4f4f]"\nPRIN1 call"[/color] wf[b][color=BLACK])[/color][/b]
 [b][color=BLACK]([/color][/b]write-line [color=#2f4f4f]" - "[/color] wf[b][color=BLACK])[/color][/b]
 [b][color=BLACK]([/color][/b]print [color=#2f4f4f]"\nPRIN1 call"[/color] wf[b][color=BLACK])[/color][/b]
 [b][color=BLACK]([/color][/b]close wf[b][color=BLACK])[/color][/b]

-David

What I am having a hard time understanding is why the \n is needed before "My name is..." I have run

(defun c:test ()

(princ "\nMy Name is \nJohn")

(princ))

and

(defun c:test ()

(princ "My Name is \nJohn")

(princ))

without seeing any difference at all. I see several examples of this when learning LISP and it is very confusing to me. Isn't the first \n redundant? Why do we put it there?

Using "\n" in larger routines will split lines between commands, providing similar behavior/appearance to native AutoCAD commands. You will not notice a difference in the example you posted.

Beeftimer, try running the following:

(defun c:test ()
   (setq e (car (entsel "\nSelect an entity : "))
         i (getpoint "Select a point : ") )
   (princ)
)

vs

(defun c:test ()
   (setq e (car (entsel "\nSelect an entity : "))
         i (getpoint "\nSelect a point : ") )
   (princ)
)

Do you notice the difference when progressing through the steps?

Try alert also for messages.

(alert (strcat "Hello" "\nworld"))

This is my get a value using a dialouge. Code (ah:getval "Enter the size" 6 5) Getval is preloaded.

;; Input  Dialog box with variable title
;; By Ah June 2012
;; original concept by Alan JT
;; code (ah:getval title width limit)

(defun AH:Getval (title width limit / fo)
(setq fname "C://acadtemp//getval.dcl")
(setq fo (open fname "w"))
(write-line "ddgetval : dialog {" fo)
(write-line " : row {" fo)
(write-line ": edit_box {" fo)
(write-line (strcat "    key = "  (chr 34) "sizze" (chr 34) ";") fo)
(write-line  (strcat " label = "  (chr 34) title (chr 34) ";"  )   fo)
; these can be replaced with shorter value etc
;(write-line "     edit_width = 18;" fo) 
;(write-line "     edit_limit = 15;" fo)
(write-line width fo) 
(write-line limit fo)
(write-line "   is_enabled = true;" fo)        
(write-line "    }" fo)
(write-line "  }" fo)
(write-line "ok_cancel;}" fo)
(close fo)

(setq dcl_id (load_dialog  "c:\\acadtemp\\getval"))
(if (not (new_dialog "ddgetval" dcl_id))
(exit))
(action_tile "sizze" "(setq item  $value)(done_dialog)")
(mode_tile "sizze" 3)
(start_dialog)
; returns the value of item
)

See if this helps :

(defun c:test ()
(princ "Line 1: ")
(princ "\nMy Name is \nJohn")
(princ))

(defun c:test ()
(princ "Line 2 : ")
(princ "My Name is \nJohn")
(princ))

-David

Yes, I do see the difference very clearly with your examples. I understood the difference between the two, but my question was regarding why it was needed in the example that I posted? From what you said, I'm leaning that, yes, the first \n is, in fact, redundant and/or unnecessary in that example? Is it just standard practice to include it there so as to create good habits?

And thank you for your response.

Using "\n" in larger routines will split lines between commands, providing similar behavior/appearance to native AutoCAD commands. You will not notice a difference in the example you posted.

 

Beeftimer, try running the following:

(defun c:test ()
   (setq e (car (entsel "\nSelect an entity : "))
         i (getpoint "Select a point : ") )
   (princ)
)

vs

 

(defun c:test ()
   (setq e (car (entsel "\nSelect an entity : "))
         i (getpoint "\nSelect a point : ") )
   (princ)
)

Do you notice the difference when progressing through the steps?

Yes, I do see the difference very clearly with your examples. I understood the difference between the two, but my question was regarding why it was needed in the example that I posted? From what you said, I'm leaning that, yes, the first \n is, in fact, redundant and/or unnecessary in that example? Is it just standard practice to include it there so as to create good habits?

And thank you for your response.

Exactly

my question was regarding why it was needed in the example that I posted? From what you said, I'm leaning that, yes, the first \n is, in fact, redundant and/or unnecessary in that example? Is it just standard practice to include it there so as to create good habits?

You can't know in advance the text which may have been previously printed to the command-line and which may obscure your printed message, hence it is usually wise to print to a new-line. For example, consider a case in which the user has evaluated your function from another program:

(defun c:test ()
(princ "My Name is \nJohn")
(princ))

[color=gray]Command:[/color] (progn (princ "\nSome random text") (c:test))
Some random textMy Name is
John

Versus:

(defun c:test ()
(princ "\nMy Name is \nJohn")
(princ))

[color=gray]Command:[/color] (progn (princ "\nSome random text") (c:test))
Some random text
My Name is
John